How to use Collections.binarySearch for ArrayList<List<String>> arr in java-CodePudding

I have an ArrayList<List<String>> and im trying to use the built-in binary search in the collection but I always come up with an error

int index = Collections.binarySearch(arraylistdata, id);

Where arraylistdata is my ArrayList of List<String>.

CodePudding user response：

public class CollectionsTest {
    
    @Test
    void test() {
        List<String> list = List.of("a", "b", "c");
        int index = Collections.binarySearch(list, "b");
        Assertions.assertEquals(1, index);
    }
}

This works fine, but you need to known that Collections#binarySearch accept a List<? extends Comparable<? super T>> as its first parameter.

While in your case, ArrayList<List<String>> does not match the requirement , as List<String> or List<?> itself is not a Comparable object.